1. Field of the Invention
This invention relates to shell and tube heat exchangers and is particularly concerned with improved exchangers provided with means for supporting the floating head in the required position adjacent the floating tube sheet during the assembly of such exchangers.
2. Description of the Prior Art
Shell and tube heat exchangers are widely used in chemical plants, petroleum refineries, steam plants and similar installations. Typically, such an exchanger includes an external shell having inlet and outlet ports for circulation of the shell-side fluid, an elongated bundle of tubes positioned within the shell, and transverse baffles for directing the shell-side fluid back and forth across the tubes. The tubes are supported by tube sheets, one of which is normally stationary and the other of which may be either stationary or "floating" to accommodate changes in tube length due to thermal expansion. The tube bundle and shell may be arranged so that the tube-side fluid makes a single pass through the shell or instead makes two or more passes. In a single pass exchanger, the tube-side fluid in introduced into a head at one end of the shell and withdrawn from a second head at the other end. In a multiple pass unit, the exchanger will generally be provided with one head containing one or more baffles so that the tube-side fluid can be introduced into one portion of the head and withdrawn from another portion. A second head containing one or more baffles which divert the tube-side fluid from one set of tubes into another will generally be located at the other end of the tube bundle. A wide variety of different shell and tube arrangements have been employed in the past.
Multiple pass shell and tube exchangers are often furnished with one fixed and one floating tube sheet, the floating tube sheet being fitted with a return or floating head. In order to reduce costs and increase the effectiveness of such exchangers, most floating heads are connected to the floating tube sheet by a clamp arrangement. An integral circular flange on the floating head and a split circular flange or ring make up the clamp. These pieces are bolted together with the floating tube sheet positioned between them, all of the connecting bolts being located beyond the outer edge of the tube sheet. A circular gasket is fitted between the floating head flange and tube sheet to prevent leakage.
The assembly of a unit of the type referred to above frequently presents difficulties. For proper leakfree operation, all of the parts must be precisely located when the final bolt tightening operation has been completed. The floating head-split ring assembly is normally free to rotate about the entire tube sheet and, since the split ring and floating head completely cover the tube sheet, must be positioned on the tube sheet without any reference marks or other guides to aid in its proper placement. Moreover, the parts are generally heavy and difficult to handle. This complicates the problem of positioning the head on the tube sheet with the precision necessary and often leads to the assembly of exchangers with the parts misaligned. Misfits, mechanical damage to the floating head and tube sheet, leakage of the joint, and extended installation time often result. These are not only costly but also hazardous, particularly in the case of exchangers intended for the handling of fluids at high temperatures and high pressures.